1. Field of the Invention
The present invention relates to a system for and a method of detecting electrically reverse packaging of a PROM when the PROM is packaged on a socket.
2. Prior Art
A conventional method of and apparatus for detecting reverse packaging of a programmable read-only memory (hereinafter referred to as PROM) will be described with reference to FIG. 4.
Desginated at 2 is a socket, 6 is a detecting circuit and 7 is judging means.
The PROM is packged on the socket 2. In FIG. 4, the detecting circuit 6 is connected to a terminal 2D of the socket 2.
The relation between the socket 2 and the detecting circuit 6 will be described with reference to FIG. 5.
Designated at 5 is a PROM having an impedance 5F interposed between pins 5C and 5D. In FIG. 5, a parasitic diode is illustrated as the impedance 5F. The pin 5C of the PROM 5 is inserted into a ground terminal 2C of the socket 2 and the pin 5D of the PROM 5 is inserted into terminal 2D of the socket 2. The detecting circuit 6 is connected to the terminal 2D of the socket 2. A reference voltage is applied to one of the input terminals of a comparator 6A of the detecting circuit 6 and an output voltage of the socket 2 supplied from the terminal 2D and -5 V are applied to another input terminal 6C of the detecting circuit 6. The resultant comparison value is supplied from the output of the comparator 6A to the judging means 7.
The circuit as illustrated in FIG. 5 is illustrated in FIG. 2 of the Japanese Utility Model Application No. 63-36998.
The step of judging the packaging state of the PROM 5 by the judging means 7 is illustrated in the flow-chart of FIG. 6.
In Step 8, the judging means 7 judges as to whether the PROM 5 is packaged in the socket 2. If the reference voltage of the detecting circuit 6 to be applied to the input terminal 6B of the comparator 6A is 4 V and the output voltage of the socket 2 supplied from the terminal 2D is at least -4 V, it is judged that the PROM 5 is not packaged in the socket 2 and it is judged that the PROM 5 is packaged in other case.
In Step 9, the judging means 7 judges as to whether the PROM 5 is reversely packaged in the socket 2. If the reference voltage of the detecting circuit 6 to be applied to the input terminal 6B is -1 V and the output voltage of the socket 2 applied from the terminal 2D is at least -1 V, it is judged that the PROM 5 is reversely packaged in the socket 2 and it is judged that the PROM 5 is reversely packaged in other case.
However, there has been such a problem in the steps of judging as illustrated in FIG. 6 that it is not judged as to whether the PROM having different impedances is packaged or not packaged in the socket 2 since it has been judged whether the PROM 5 is packaged or not and whether the PROM 5 is normally packaged or reversely packaged with use of the two reference voltages, i.e. 4 V and -1 V.